1. Field of the Invention
The present invention relates to semiconductor devices, and in particular, to a metal-oxide-semiconductor (MOS) device with an isolated drain and a method for fabricating the same.
2. Description of the Related Art
Battery-operated electronic systems such as notebook personal computers, personal digital assistants, and wireless communication devices often use power MOS (metal oxide semiconductor) devices as low on-resistance electronic switches for distributing battery power. For battery-operated applications, low on-resistance can be particularly important to ensure as little power consumption on the battery as possible. This ensures long battery life.
FIG. 1 is an electrical schematic of a conventional buck converter for power management of an electronic system. During operation, when both a high-side MOS device 12 and a low-side MOS device 10 turn off, in order to keep the current in inductor 14 continuous, a body diode and a substrate diode (both not shown) in the low-side MOS device 10 will turn on to support this current. However, undesired substrate current injections happen due to the action of turning on the substrate diode in the low-side MOS device 10, such that noises for causing latch-up or other circuit function failures may thus affect the control circuitry 20 of the electronic system.